The present invention relates generally to analyte test sensors and more particularly to a novel array of analyte test sensors.
There are many medical conditions which require frequent measurement of the concentration of a particular analyte in the blood of a patient. For example, diabetes is a disease which typically requires a patient to routinely measure the concentration of glucose in his/her blood. Based upon the results of each blood glucose measurement, the patient may then require a particular drug treatment (e.g., an injection of insulin) in order to regulate that the blood glucose level of the patient remains within a specified range. Exceeding the upper limit of said range (hyperglycemia) or dropping beneath the lower limit of said range (hypoglycemia) should be avoided with as much diligence as possible to prevent the patient from experiencing serious medical complications which include, inter alia, retinopathy, nephropathy, and neuropathy.
A multi-step process is commonly practiced by diabetes patients to self-monitor the level of glucose present in their blood.
In the first step of said process, a patient is required to provide a blood sample suitable for testing. Blood samples taken from a patient for blood sugar monitoring are typically obtained by piercing the skin of the patient using a lancet device. A lancet device typically includes a body and a lancet. The body is typically adapted to be held by the user, the lancet being coupled to the body and being adapted to penetrate through the epidermis (the outermost layer of the skin) of the patient and into the dermis (the layer of skin directly beneath the epidermis) which is replete with capillary beds. The puncture of one or more capillaries by the lancet generates a sample of blood which exits through the incision in the patient's skin.
In some lancet devices, the lancet extends from the body at all times. In other lancet devices, the lancet is adapted to be moved, when actuated, from a retracted position in which the lancet tip is disposed within the body to an extended position in which the lancet tip extends beyond the body. Typically, the movement of the lancet from its retracted position to its extended position is effected with such force that contact of the moving lancet tip with the skin of a patient results in the piercing of the skin of the patient. In many such lancet devices having a movable lancet, the lancet is automatically drawn back into the body after reaching its extended position (e.g., using a spring) in order to minimize the risk of inadvertent lancet sticks.
In the second step of said process, a blood glucose monitoring system is utilized to measure the concentration of glucose in the blood sample. One type of glucose monitoring system which is well known and widely used in the art includes a blood glucose meter (also commonly referred to a blood glucose monitor) and a plurality of individual, disposable, electrochemical test sensors which can be removably loaded into the meter. Examples of blood glucose monitoring systems of this type are manufactured and sold by Abbott Laboratories, Medisense Products of Bedford, Mass. under the PRECISION line of blood glucose monitoring systems.
Each individual electrochemical test sensor typically includes a substrate which is formed as a thin, rectangular strip of non-conductive material, such as plastic. A plurality of carbon-layer electrodes are deposited (e.g., screen printed) on the substrate along a portion of its length in a spaced apart relationship, one electrode serving as the reference electrode for the test sensor and another electrode serving as the working electrode for the test sensor. All of the conductive electrodes terminate at one end to form a reaction area for the test sensor. In the reaction area, an enzyme is deposited on the working electrode. When exposed to the enzyme, glucose present in a blood sample undergoes a chemical reaction which produces a measurable electrical response. The other ends of the electrical contacts are disposed to electrically contact associated conductors located in the blood glucose monitor, as will be described further below.
A blood glucose monitor is typically modular and portable in construction to facilitate its frequent handling by the patient. A blood glucose monitor often comprises a multi-function test port which is adapted to receive the test sensor in such a manner so that an electrical communication path is established therebetween. As such, an electrical reaction created by depositing a blood sample onto the reaction area of the test sensor travels along the working electrode of the test sensor and into the test port of the blood glucose monitor. Within the housing of the monitor, the test port is electrically connected to a microprocessor which controls the basic operations of the monitor. The microprocessor, in turn, is electrically connected to a memory device which is capable of storing a multiplicity of blood glucose test results.
In use, the blood glucose monitoring system of the type described above can be used in the following manner to measure the glucose level of a blood sample and, in turn, store the result of said measurement into memory as test data. Specifically, a disposable test sensor is unwrapped from its packaging and is inserted into the test port of the monitor. With the test sensor properly inserted into the monitor, there is established a direct electrical contact between the conductors on the test sensor and the conductors contained within the test port, thereby establishing an electrical communication path between the test sensor and the monitor. Having properly disposed the test sensor into the test port, the monitor typically displays a “ready” indication on its display.
The user is then required to provide a blood sample using a lancet device. Specifically, a disposable lancet is unwrapped from its protective packaging and is loaded into a corresponding lancet device. The lancet device is then fired into the skin of the patient to provide a blood sample.
After lancing the skin, the patient is required to deposit one or more drops of blood from the patient's wound site onto the reaction area of the test sensor. When a sufficient quantity of blood is deposited on the reaction area of the test sensor, an electrochemical reaction occurs between glucose in the blood sample and the enzyme deposited on the working electrode which, in turn, produces an electrical current which decays exponentially over time. The decaying electrical current created through the chemical reaction between the enzyme and the glucose molecules in the blood sample, in turn, travels along the electrically conductive path established between the test sensor and the monitor and is measured by the microprocessor of the monitor. The microprocessor of the monitor, in turn, correlates the declining current to a standard numerical glucose value (e.g., using a scaling factor). The numerical glucose value calculated by the monitor is then shown on the monitor display for the patient to observe. In addition, the data associated with the particular blood glucose measurement is stored into the memory for the monitor.
A principal drawback associated with blood glucose monitoring systems of the type described above is that the above-described glucose measurement procedure requires multiple preparatory steps prior to each assay. Specifically, prior to performing each blood glucose measurement, a patient is required to unwrap an individual, disposable test sensor and, subsequent thereto, install the unwrapped sensor into the test port of the blood glucose test monitor. As can be appreciated, the fact that the aforementioned process fails to provide the user with a continuous means for performing multiple assays significantly increases the overall complexity and manual dexterity which is required to use such a system, which is highly undesirable.
Accordingly, it is known in the art for a multiplicity of individual test sensors to be integrated into a single sensor array. In this manner, with the sensor array properly installed into a compatible blood glucose meter, a plurality of individual tests can be performed without necessitating the user to unwrap, install and discard individual test sensors. Rather, the meter is designed to sequentially index each sensor in the array into a testing position within the meter prior to performing an individual assay. Once all of the test sensors on the sensor array have been used, the sensor array can be replaced to allow for future continuous testing.
It should be noted that sensor arrays are commonly constructed in a number of different configurations.
As an example, it is well known for sensor arrays to be constructed in the form of a disc-shaped cartridge which includes a plurality of individual test sensors that are radially arranged along its outer periphery. In this manner, with the sensor array properly installed into a compatible meter, the continuous, incremental rotation of the sensor array serves to sequentially index each successive test sensor into the proper testing position within the meter in order to perform an assay. An example of a sensor array constructed in the form of a disc-shaped cartridge is shown in U.S. Pat. No. 5,741,634 to Y. Nozoe et al.
As another example, it is well known for sensor arrays to be constructed in the form of a continuous, elongated strip which includes a plurality of individual test sensors that are linearly arranged in an end-to-end relationship. In this manner, with the sensor array properly installed into a compatible meter, the continuous, incremental linear displacement of the sensor array serves to sequentially index each successive test sensor into the proper testing position within the meter in order to perform an assay. Examples of a sensor array constructed in the form of a continuous, elongated strip are shown in U.S. Pat. No. 5,395,504 to E. Saurer et al. and U.S. Pat. No. 5,074,977 to P. W. Cheung et al.
Although useful in performing multiple continuous glucose measurements, sensor arrays of the type described above suffer from a notable drawback. Specifically, sensor arrays of the type described above are typically constructed with a limited degree of flexibility and/or bendability. Due to their relative rigidity, the sensor arrays are only capable of movement along a single plane (e.g., either through rotation or linear displacement). As a result, these types of sensor arrays often preclude design engineers from constructing a complementary meter of reduced size and/or mechanical complexity, which is highly undesirable.